In the system integration manual of the Leon G100 GSM modem (http://www.u-blox.com/images/downloads/Product_Docs/LEON-G1-G2_SystemIntegrationManual_(UBX-13002023).pdf) it’s written to carefully design the 50 Ohm micro strip or stripline on the pcb (“The transmission line up to antenna connector or pad may be a micro strip or a stripline. In any case must be designed to achieve 50 Ω characteristic impedance”). I design a 2-layer pcb and before I got to chapter 18.104.22.168 of the mentioned document I carelessly attached the ANT with the signal pin of the SMA.
I cannot use the stripline as it’s a 2-layer PCB, instead I used a coplanar waveguide with ground. Using a KiCad Pcb Calculator I ended up with the following conclusions: to have 50 Ohm at FR4 PCB of 1.5mm thickness and freq of 900MHz it has to be a 1.25mm wide path separated from the gnd paths by 0.25mm. The Electrical length 22 degrees.
And here I have some questions: - for which frequency, 900 or 1800MHz shall I calculate the parameters? - what is the 22 degrees electrical length about?. This value increases proportionally with frequency and at 1800MHz I get 44 degrees - how shall I design the vias for the gnd and sma signal pin? As far as I know the SMA connector is “through pcb” not SMD.